This section provides background information related to the present disclosure which is not necessarily prior art.
Galvanic protection in vehicle components formed of dissimilar materials (e.g., different metal materials or metal/composite materials) can pose various challenges. In applications where the dissimilar materials are typically submerged or immersed in an electrolyte, galvanic protection need only be generally placed in electrical contact with the susceptible metal(s) and electrolyte. Thus, typical sacrificial anodes on an immersed vessel are not geometrically specific. For example, nautical ships, boats, and other vessels may have a single sacrificial anode attached to a submerged portion of the hull in contact with saltwater or fresh water, which serves to galvanically protect the entire ship. Thus, where the electrolyte is typically in continuous contact with the dissimilar materials, non-localized galvanic protection is possible.
However, galvanic protection in vehicles that are not submerged in an electrolyte, but rather may have dissimilar materials intermittently exposed to potential electrolytes pose particular challenges. Such vehicles may include automobiles, snowmobiles, motorcycles, and the like. Current approaches typically include corrosion protection by coating or otherwise insulating components from contact with one another. The general concept of such galvanic corrosion is to avoid creating an electrically conductive path between dissimilar materials when an electrolyte is present. For example, corrosion protection coatings may include electrically inert or insulating coatings, such as passivation layers and the like, or may involve physically separating the dissimilar materials. This is particularly true for applications that employ carbon-fiber composite materials near metal materials in metal vehicle components, such as metal structural members or frames.
Carbon containing materials, such as composite materials like carbon fiber reinforced plastics (CFRP) are generally considered to be galvanically incompatible with metal materials. Carbon serves as an efficient cathode and thus in the past, galvanic protection has focused on completely isolating the carbon containing material from nearby metals. However, use of coatings and other isolation techniques in dissimilar materials that employ carbon fiber composites can potentially still be vulnerable to galvanic corrosion over time, especially in non-marine environments where galvanic corrosion is intermittent and localized. For example, corrosion protection coatings applied to one or both of the dissimilar materials may have weakly adhered regions or minor manufacturing defects, such as fish eyes, pinholes, fissures, or cracks, which over long durations expose the underlying material and can concentrate corrosion therein. Furthermore, even if a corrosion protection coating has no weak or vulnerable regions whatsoever, fastening the dissimilar materials together (e.g., via mechanical fasteners, welding, or adhesives) disturbs the corrosion protection coatings and provides potential corrosion pathways.
Thus, additional techniques for galvanic protection of assemblies of components employing dissimilar materials, such as carbon containing composites and metals, would be highly desirable to improve reliability and reduce susceptibility to failure for such parts.